1. Field of the Invention
The present invention relates to a method of correcting an imbalance in an imaging device used in a digital camera or the like. More specifically, the present invention relates to a method of correcting an imbalance in an imaging device having a plurality of output terminals from which data is simultaneously read, by averaging output levels of image data respectively output from the plurality of output terminals, so that a seam will not be apparent in an image formed by combining the output data.
2. Description of the Related Art
In order to improve the ability of sequence shooting in a conventional digital camera system on the order of ten frames per second, it is required that the overall system be improved. That is, there must be an improvement of the speed of reading from the imaging device and of the speed of writing data from the imaging device to a frame memory.
FIG. 1 schematically shows the construction of an imaging device, more specifically a CCD with two horizontal CCD sections and two outputs, which is an example of improvement of conventional technology.
In the CCD shown in FIG. 1, charges generated by photodiodes 9 at respective pixels are simultaneously transferred to vertical CCD segments 10 at a predetermined timing, and the charges transferred to the vertical CCD segments 10 are transferred, line by line, to horizontal CCD segments 7 and 8 at a subsequent timing.
The horizontal CCD segments 7 transfer the charges that have been transferred thereto to a left amp 5 in synchronization with a transfer clock, whereas the horizontal CCD segments 8 transfer the charges that have been transferred thereto to a right amp 4 in synchronization with the transfer clock. Thus, image data captured by the CCD is read as left and right segments separated along a center of the screen.
The left and right parts of the image data captured by the CCD are respectively input to CDS/AGC circuits 3 and 6, which are grounded via resistors 1 and 2, respectively, and A/D conversion circuits 116 and 117 (shown in FIG. 2), and then stored in frame memories 126 and 127 (shown in FIG. 3) after being converted into digital data. These digital image data for the left part and for the right part are imbalanced mainly due to a difference in gain between the CDS/AGC circuits 3 and 6, particularly with regard to the offset component and the gain component. In order to correct the imbalance, calibration imaging is performed in addition to main imaging.
In an imaging apparatus such as a digital camera, in a proposed method, calibration imaging for calculating a correction coefficient for correcting an imbalance among a plurality of outputs is performed before or after the main imaging, and an imbalance among a plurality of outputs in an image obtained by main imaging is corrected using the correction coefficient. In another proposed method, the imbalance is corrected by the correlation of a plurality of outputs after converting a plurality of output signals into digital image data by an analog/digital converter.
However, some high-specification digital cameras, for example, of the single lens reflex type, allow various settings of imaging conditions, such as speed setting equivalent to ISO 100 to ISO 6400 or long-time imaging exceeding ten seconds. Thus, the correction methods described above are not sufficient for all these imaging conditions, resulting in inaccurate or unstable correction.